Buck-Boost Converter

Controller-driven DC-DC inverting or four-switch step-up or step-down voltage regulator

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Libraries:
Simscape / Electrical / Semiconductors & Converters / Converters

Description

The Buck-Boost Converter block represents a DC-DC converter that can either step up or step down DC voltage from one side of the converter to the other as driven by an attached controller and gate-signal generator. Buck-boost converters are also known as step-up/step-down voltage regulators because they can increase or decrease voltage magnitude.

The block can also invert voltage so that the polarity of the output voltage is the opposite of the polarity of the input voltage. The magnitude of the output voltage depends on the duty cycle.

The Buck-Boost Converter block allows you to model an inverting buck-boost converter with one switching device or a buck-boost converter with four switching devices. Options for the type of switching devices are:

• GTO — Gate turn-off thyristor. For information about the I-V characteristic of the device, see GTO.

• Ideal semiconductor switch — For information about the I-V characteristic of the device, see Ideal Semiconductor Switch.

• IGBT — Insulated-gate bipolar transistor. For information about the I-V characteristic of the device, see IGBT (Ideal, Switching).

• MOSFET — N-channel metal-oxide-semiconductor field-effect transistor. For information about the I-V characteristic of the device, see MOSFET (Ideal, Switching).

• Thyristor — For information about the I-V characteristic of the device, see Thyristor (Piecewise Linear).

• Averaged Switch — Semiconductor switch with an antiparallel diode. The control signal port G accepts values in the interval [0,1]. When G is equal to 0 or 1, the averaged switch is fully opened or fully closed respectively. The switch behaves similarly to the Ideal Semiconductor Switch block with an antiparallel diode. When G is between 0 and 1, the averaged switch is partly opened. You can average the pulse-width modulation (PWM) signal over a specified period. You can then undersample the model and use modulation waveforms instead of PWM signals.

Converter Topology

You can model this converter as an inverting buck-boost converter with a physical signal gate control port or with two electrical control ports, or as a four-switch buck-boost converter with an electrical control port. To select the converter topology, set the Modeling option parameter to either:

• Inverting converter — Inverting buck-boost converter with physical or electrical gate control port.

• Four-switch converter — Four-switch buck-boost converter with multiplexed gate signals.

The inverting converter models contain a switching device, a diode, an inductor, and an output capacitor.

The four-switch converter model contains four switching devices, an inductor, and an output capacitor.

In each case, the capacitor smoothes the output voltage.

Protection

You can include a snubber circuit for each switching device. Snubber circuits contain a series-connected resistor and capacitor. They protect switching devices against high voltages that inductive loads produce when the device turns off the voltage supply to the load. Snubber circuits also prevent excessive rates of current change when a switching device turns on.

To include and configure a snubber circuit for each switching device, use the Snubbers parameters.

Gate Control

To connect gate-control voltage signals to the gate ports of the switching devices, for the:

• Inverting converter model:

  • PS control port model:

    1. Convert a Simulink^® gate-control voltage signal to a physical signal using a Simulink-PS Converter block.

    2. Connect the Simulink-PS Converter block to the G port.

  • Electrical control ports model:

    1. Connect a Simscape™ electrical-domain positive DC voltage signal to the G+ port.

    2. Connect the Simscape electrical-domain negative DC voltage signal to the G- port.

• Synchronous converter model:

  1. Convert each Simulink gate-control voltage signal to a physical signal using Simulink-PS Converter blocks.

  2. Multiplex the converted gate-control signals into a single vector using a Four-Pulse Gate Multiplexer

  3. Connect the vector signal to the G port.

Piecewise Constant Approximation in Averaged Switch for FPGA Deployment

If you set the Switching device parameter to Averaged switch and your model uses a partitioning solver, this block produces nonlinear partitions because the average mode equations include modes, G_sat that are functions of the input G. To make these equations compatible with hardware description language (HDL) code generation, and therefore FPGA deployment, set the Integer for piecewise constant approximation of gate input (0 for disabled) parameter to a value greater than 0. This block then treats the G_sat mode as a piecewise constant integer with a fixed range. This turns the previously nonlinear partitions to linear time varying partitions.

An integer value in the range [0,K], where K is the value of the Integer for piecewise constant approximation of gate input (0 for disabled), is now associated with each real value mode in the range [0,1]. The block computes the piecewise constant mode by dividing the original mode by K to normalize it back to the range [0,1]:

$$\begin{array}{l}{u}_I=\left(floor\left(u\cdot K\right)\right)\\ \widehat{u}=\frac{u_I}{K}\end{array}$$

Variables

To set the priority and initial target values for the block variables before simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. You can specify nominal values using different sources, including the Nominal Values section in the block dialog box or Property Inspector. For more information, see System Scaling by Nominal Values.

Examples

Inverting Topology Buck-Boost Converter Control

Control the output voltage of an inverting topology buck-boost converter. The inverting topology buck-boost converter uses only a single switch and the output voltage is of the opposite polarity than the input. To adjust the duty cycle, the Control subsystem uses a PI-based control algorithm. The input voltage and the system load are considered constant throughout the simulation. The total simulation time (t) is 0.25 seconds. At t = 0.15 seconds, the voltage reference changes and the system switches from buck mode to boost mode.

• Open Model

Four-Switch Buck-Boost Converter Control

Control the output voltage of a four-switch buck-boost converter. To adjust the duty cycle, the Control subsystem uses a PI-based control algorithm. In both the boost and buck modes, one switch controls the duty cycle, one is operated inversely and the other two are kept in fix positions. The input voltage and the system load are considered constant throughout the simulation. The total simulation time (t) is 0.25 seconds. At t = 0.15 seconds, the voltage reference changes and the system switches from buck mode to boost mode.

• Open Model

Assumptions and Limitations

Only a PWM-driven averaged switch converter captures both continuous conduction mode (CCM) and discontinuous conduction mode (DCM). A duty cycle-driven averaged switch converter captures CCM only.

Ports

Input

G — Switching device gate control

physical signal | scalar

Physical signal port associated with the gate terminals of the switching device.

Dependencies

To enable this port, set Modeling option to Inverting converter and Gate-control port to PS.

Data Types: double

Conserving

G — Switching device gate control

electrical | vector

Electrical conserving port associated with the gate terminals of the switching devices.

Dependencies

To enable this port, set Modeling option to Four-switch converter.

Data Types: double

G+ — Switching device gate control positive terminal

electrical | scalar

Positive electrical conserving port associated with the positive gate terminal of the switching device.

Dependencies

To enable this port, set Modeling option to Inverting converter and Gate-control port to Electrical.

Data Types: double

G- — Switching device gate control negative terminal

electrical | scalar

Negative electrical conserving port associated with the negative gate terminal of the switching device.

Dependencies

To enable this port, set Modeling option to Inverting converter and Gate-control port to Electrical.

Data Types: double

1+ — Positive DC voltage 1

electrical | scalar

Electrical conserving port associated with the positive terminal of the first DC voltage.

Data Types: double

1- — Negative DC voltage 1

electrical | scalar

Electrical conserving port associated with the negative terminal of the first DC voltage.

Data Types: double

2+ — Positive DC voltage 2

electrical | scalar

Electrical conserving port associated with the positive terminal of the second DC voltage.

Data Types: double

2- — Negative DC voltage 2

electrical | scalar

Electrical conserving port associated with the negative terminal of the second DC voltage.

Data Types: double

Parameters

Modeling option — Whether to model inverting or four-switch buck-boost converter

Inverting converter (default) | Four-switch converter

Whether to model an inverting or a four-switch buck-boost converter.

Switching Devices

This table shows how the visibility of Switching Devices parameters depends on the Switching device that you select. To learn how to read the table, see Parameter Dependencies.

Switching Devices Parameter Dependencies

Parameters and Options
Switching device
Ideal Semiconductor Switch	GTO	IGBT	MOSFET	Thyristor	Averaged Switch
On-state resistance	Forward voltage	Forward voltage	Drain-source on resistance	Forward voltage	On-state resistance
Off-state conductance	On-state resistance	On-state resistance	Off-state conductance	On-state resistance
Threshold voltage	Off-state conductance	Off-state conductance	Threshold voltage	Off-state conductance
	Gate trigger voltage, Vgt	Threshold voltage		Gate trigger voltage, Vgt	Integer for piecewise constant approximation of gate input (0 for disabled)
	Gate turn-off voltage, Vgt_off			Gate turn-off voltage, Vgt_off
	Holding current			Holding current

Gate-control port — Whether to specify physical or electrical control port for the switching gate

PS (default) | Electrical

Whether to specify physical or electrical control port for the switching gate.

Dependencies

To enable this port, set Modeling option to Inverting converter.

Switching device — Switch type

Ideal Semiconductor Switch (default) | GTO | IGBT | MOSFET | Thyristor | Averaged Switch

Switching device type for the converter. For the four-switch model, the switches are identical.

model.

Dependencies

See the Switching Devices Parameter Dependencies table.

Forward voltage — Voltage

0.8 V (default) | scalar

For the different switching device types, the Forward voltage is taken as:

• GTO — Minimum voltage required across the anode and cathode block ports for the gradient of the device I-V characteristic to be 1/R_on, where R_on is the value of On-state resistance

• IGBT — Minimum voltage required across the collector and emitter block ports for the gradient of the diode I-V characteristic to be 1/R_on, where R_on is the value of On-state resistance

• Thyristor — Minimum voltage required for the device to turn on

Dependencies

See the Switching Devices Parameter Dependencies table.

On-state resistance — Resistance

0.001 Ohm (default) | scalar

For the different switching device types, the On-state resistance is taken as:

• GTO — Rate of change of voltage versus current above the forward voltage

• Ideal semiconductor switch — Anode-cathode resistance when the device is on

• IGBT — Collector-emitter resistance when the device is on

• Thyristor — Anode-cathode resistance when the device is on

• Averaged switch — Anode-cathode resistance when the device is on

Dependencies

See the Switching Devices Parameter Dependencies table.

Drain-source on resistance — Resistance

0.001 Ohm (default) | scalar

Resistance between the drain and the source, which also depends on the gate-to-source voltage.

Dependencies

See the Switching Devices Parameter Dependencies table.

Off-state conductance — Conductance

1e-5 1/Ohm (default) | scalar

Conductance when the device is off. The value must be less than 1/R, where R is the value of On-state resistance.

For the different switching device types, the On-state resistance is taken as:

• GTO — Anode-cathode conductance

• Ideal semiconductor switch — Anode-cathode conductance

• IGBT — Collector-emitter conductance

• MOSFET — Drain-source conductance

• Thyristor — Anode-cathode conductance

Dependencies

See the Switching Devices Parameter Dependencies table.

Threshold voltage — Voltage threshold

6 V (default) | scalar

Gate voltage threshold. The device turns on when the gate voltage is above this value. For the different switching device types, the device voltage of interest is:

• Ideal semiconductor switch — Gate-cathode voltage

• IGBT — Gate-emitter voltage

• MOSFET — Gate-source voltage

Dependencies

See the Switching Devices Parameter Dependencies table.

Gate trigger voltage, Vgt — Voltage threshold

1 V (default) | scalar

Gate-cathode voltage threshold. The device turns on when the gate-cathode voltage is above this value.

Dependencies

See the Switching Devices Parameter Dependencies table.

Gate turn-off voltage, Vgt_off — Voltage threshold

-1 V (default) | scalar

Gate-cathode voltage threshold. The device turns off when the gate-cathode voltage is below this value.

Dependencies

See the Switching Devices Parameter Dependencies table.

Holding current — Current threshold

1 A (default) | scalar

Gate current threshold. The device stays on when the current is above this value, even when the gate-cathode voltage falls below the gate trigger voltage.

Dependencies

See the Switching Devices Parameter Dependencies table.

Integer for piecewise constant approximation of gate input (0 for disabled) — Integer mode for FPGA deployment

0 (default) | nonnegative scalar

Integer used to perform piecewise constant approximation of the gate input for FPGA deployment.

Dependencies

To enable this parameter, set Switching device to Averaged Switch.

Diode

This table shows how the visibility of Diode parameters depends on how you configure the Model dynamics and Reverse recovery time parameterization parameters. To learn how to read this table, see Parameter Dependencies.

Diode Parameter Dependencies

Parameters and Options
Model dynamics
Diode with no dynamics	Diode with charge dynamics
Forward voltage	Forward voltage
On resistance	On resistance
Off conductance	Off conductance
	Junction capacitance
	Peak reverse current, iRM
	Initial forward current when measuring iRM
	Rate of change of current when measuring iRM
	Reverse recovery time parameterization
	Specify stretch factor	Specify reverse recovery time directly	Specify reverse recovery charge
	Reverse recovery time stretch factor	Reverse recovery time, trr	Reverse recovery charge, Qrr

Model dynamics — Diode model

Diode with no dynamics (default) | Diode with charge dynamics

Diode type. The options are:

• Diode with no dynamics — Select this option to prioritize simulation speed using the Diode block.

• Diode with charge dynamics — Select this option to prioritize model fidelity in terms of reverse mode charge dynamics using the commutation diode model of the Diode block.

Note

If you select Averaged Switch for the Switching Device parameter in the Switching Device setting, this parameter is not visible and Diode with no dynamics is automatically selected.

Dependencies

See the Diode Parameter Dependencies table.

Forward voltage — Voltage

0.8 V (default) | scalar

Minimum voltage required across the positive and negative block ports for the gradient of the diode I-V characteristic to be 1/R_on, where R_on is the value of On resistance.

On resistance — Resistance

0.001 Ohm (default) | scalar

Rate of change of voltage versus current above the Forward voltage.

Off conductance — Conductance

1e-5 1/Ohm (default) | scalar

Conductance of the reverse-biased diode.

Junction capacitance — Capacitance

50 nF (default) | scalar

Diode junction capacitance.

Dependencies

See the Diode Parameter Dependencies table.

Peak reverse current, iRM — Current

-235 A (default) | scalar less than 0

Peak reverse current measured by an external test circuit.

Dependencies

See the Diode Parameter Dependencies table.

Initial forward current when measuring iRM — Current

300 A (default) | scalar greater than 0

Initial forward current when measuring peak reverse current. This value must be greater than zero.

Dependencies

See the Diode Parameter Dependencies table.

Rate of change of current when measuring iRM — Current change rate

-50 A/us (default) | scalar

Rate of change of current when measuring peak reverse current.

Dependencies

See the Diode Parameter Dependencies table.

Reverse recovery time parameterization — Recovery-time model

Specify stretch factor (default) | Specify reverse recovery time directly | Specify reverse recovery charge

Model for parameterizing the recovery time. When you select Specify stretch factor or Specify reverse recovery charge, you can specify a value that the block uses to derive the reverse recovery time.

Dependencies

See the Diode Parameter Dependencies table.

Reverse recovery time stretch factor — Stretch factor

3 (default) | scalar greater than 1

Value that the block uses to calculate Reverse recovery time, trr. Specifying the stretch factor is an easier way to parameterize the reverse recovery time than specifying the reverse recovery charge. The larger the value of the stretch factor, the longer it takes for the reverse recovery current to dissipate.

Dependencies

See the Diode Parameter Dependencies table.

Reverse recovery time, trr — Time

15 us (default) | scalar

Interval between the time when the current initially goes to zero (when the diode turns off) and the time when the current falls to less than 10 percent of the peak reverse current.

The value of the Reverse recovery time, trr parameter must be greater than the value of the Peak reverse current, iRM parameter divided by the value of the Rate of change of current when measuring iRM parameter.

Dependencies

See the Diode Parameter Dependencies table.

Reverse recovery charge, Qrr — Charge

1500 s*uA (default) | scalar

Value that the block uses to calculate Reverse recovery time, trr. Use this parameter if the data sheet for your diode device specifies a value for the reverse recovery charge instead of a value for the reverse recovery time.

The reverse recovery charge is the total charge that continues to dissipate when the diode turns off. The value must be less than $$-\frac{i^2{}_{RM}}{2a}$$,

where:

• i_RM is the value specified for Peak reverse current, iRM.

• a is the value specified for Rate of change of current when measuring iRM.

Dependencies

See the Diode Parameter Dependencies table.

LC Parameters

Inductance — Inductance

1e-6 H (default) | positive scalar

Inductance.

Inductor series resistance — Inductor series resistance

0 Ohm (default) | zero or positive scalar

Series resistance of the inductor.

Capacitance — Capacitance

1e-7 F (default) | positive scalar

Capacitance.

Capacitor effective series resistance — Capacitor resistance

1e-6 Ohm (default) | zero or positive scalar

Series resistance of the capacitor.

Snubbers

The Snubbers parameters tab is not visible if you set Switching device to Averaged Switch.

The table summarizes the Snubbers parameter dependencies. To learn how to read the table, see Parameter Dependencies.

Snubbers Parameter Dependencies

Snubbers Parameter Dependencies
Snubber
None	RC Snubber
	Snubber resistance
	Snubber capacitance

Snubber — Snubber model

None (default) | RC snubber

Switching device snubber.

Dependencies

See the Snubbers Parameter Dependencies table.

Snubber resistance — Resistance

0.1 (default) | Ohm | scalar

Resistance of the switching device snubber.

Dependencies

See the Snubbers Parameter Dependencies table.

Snubber capacitance — Capacitance

1e-7 (default) | F | scalar

Capacitance of the switching device snubber.

Dependencies

See the Snubbers Parameter Dependencies table.

References

[1] Trzynadlowski, A. M. Introduction to Modern Power Electronics, 2nd Edition. Hoboken, NJ: John Wiley & Sons Inc., 2010.

[2] Xiaoyong, R., Z. Tang, X. Ruan, J. Wei and G. Hua. Four Switch Buck-Boost Converter for Telecom DC-DC power supply applications. Twenty-Third Annual IEEE Applied Power Electronics Conference and Exposition. Austin, TX: 2008, pp 1527-1530.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2018a